Note: Descriptions are shown in the official language in which they were submitted.
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POLYOLEFIN RIBBON HAVING
REMOISTENABLE ADHESIVE BONDED THERETO
This invention relates to specially coated polyolefin
ribbons or webs which have the desirable property of remoisten-
ability and can be produced without the necessity of expensive
physical treatment of the ribbon or web prior to application of a
remoistenable a&esive. More particularly, it is concerned with
such ribbons or the like which preferably include a primer layer
bonded directly to the untreated substrate, with a remoistenable
adhesive layer including polyvinyl alcohol applied over the
primer layer and bonded thereto in order to synergistically
enhance the peel and shear strengths of the completed ribbon.
Remoistenable ribbons have been used for a number of
years for gift wrappings, bows and other ribbon decorations. The
popularity of remoistenable ribbon is chiefly attributable to
the fact that it can be easily adhered to paper or itself simply
by wetting a portion of the ribbon and pressing it into engage-
ment with the adherence area. Thus, the need for pressure sen-
sitive tape and the like in producing ribbon decorations is
completely eliminated. A number of ribbon substrates have been
used in the past in producing remoistenable ribbons. The most
common in use today are made of rayon or acetate, but these
materials are sometimes difficult to obtain and are relatively
expensive.
Polyolefin ribbons are also well-known in the art, and
have the advantage of wide availability and relative cheapness.
However, such polyolefin ribbons (principally polyethylene and
polypropylene) are generally considered to be unsuitable for
producing remoistenable ribbons because of their chemical inert-
ness and extremely low surface energy. While these properties
are advantageous in many applications, they present serious
problems when it is desired to adhere a coating such as
(Docket No. F-15617) -1-
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printing ink, metal foils, paints or adhesives to a polyolefin
web. This problem has been overcome in the past by pretreating
the web surface to raise its surface energy and create more
chemically active sites. For example, it has been known to treat
polyolefin webs by chemical etching, flame treatment, corona dis-
charge and surface abrading techniques to make possible applica-
tion of coatings and the like. However, these expedients are
time-consuming and expensive, and the resultant pretreated sur-
faces are still extremely hydrophobic and not appreciably recep-
tive to water-based adhesive systems such as those commonly used
in making remoistenable ribbons. Hence, there has heretofore
been really no acceptable way of making a remoistenable poly-
olefin ribbon.
In addition to decorative ribbons, many other types of
polyolefin substrates could advantageously be coated with a
remoistenable adhesive. For example, polyolefin webs or sheets
used in making food storage bags or a wide variety of other items
could be coated with remoistenable adhesives, if an economically
acceptable method of effective adhesive application were avail-
able. Thus, it is to be understood that the methods hereinafterdescribed can be used in a large number of instances where pro-
vision of a remoistenabIe adhesive is beneficial.
It is therefore the most important object of the
present invention to provide a remoistenable polyolefin ribbon or
the like which has a layer of remoistenable partially hydrolyzed
polyvinyl alcohol adhesive adhered thereto in a manner to give
the resultant ribbon excellent peel and shear strengths, and
without the necessity of physical pretreatment of the polyolefin
substrate, as has heretofore been thought necessary for applying
coatings to polyolefin materials.
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As a corollary to the foregoing, another object of the
invention is to provide a remoistenable polyolefin ribbon which
includes a polyolefin (preferably polypropylene or polyethylene)
substrate material, with a primer layer applied over the sub-
strate and a remoistenable polyvinyl alcohol adhesive layer
applied over the primer layer; the primer layer is preferably
characterized by the properties of bonding both to the subætrate
and outermost remoistenable adhesive layer, in order to enhance
the desirable properties of the final ribbon.
Another object of the invention is to provide a re-
moistenable polyolefin ribbon which includes a primer layer
comprising the dried residue of an initially liquid coating
composition which includes a member selected from the group
consisting of the pressure sensitive adhesives, chlorinated
polyolefins, copolymerized olefinic vinyl acetates, and mixtures
thereof, in conjunction with a remoistenable adhesive layer which
comprises the dried residue of a coating composition which in-
cludes a solids fraction of polyvinyl alcohol dispersed in water;
in the most preferred form, a primer having ethylene vinyl ace-
tate and chIorinated polyolefin materials therein is used, and
such a primer layer has been shown to synergistically enhance the
peel and shear strengths of the resultant adhesive ribbon without
the necessity of expensive surface treatment of the underlying
polyolefin substrate.
Finally, another aim of the invention is to provide a
method of applying a remoistenable adhesive to a polyolefin
ribbon or the like which includes the steps of applying a primer
composition in liquid form to the polyolefin substrate, drying
the primer to present a dried residue layer, applying a remoist-
enable polyvinyl alcohol adhesive composition over the primer
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layer and drying the adhesive composition; treatment in thismanner provides an effective remoistenable ribbon without any
pretreatment whatsoever of the underlying substrate, and at
extremely low cost.
- In its broadest aspects, the present invention is
concerned with a remoistenable polyolefin ribbon or web which
includes a substrate formed of a conventional polyolefin mate-
rial, such as polyethylene or polypropylene, in conjunction with
-a remoistenable polyvinyl alcohol adhesive applied over and
adhered to the substrate material. This is preferably accom-
plished through the use of a primer layer applied directly to the
substrate which has the properties of bonding both to the sub-
strate and the remoistenable PVA adhesive layer.
In more detail, the polyolefin substrate may comprise
an elongated ribbon or web, or any relatively thin sheet of
polyolefin material. As indicated above, the most common and
preferred polyolefin materials are the polypropylenes and poly-
ethylenes, but it is to be understood that any essentially
polyolefin material can be used in the context of the present
invention; furthermore, the invention is not limited to decora-
tive ribbons or the like, but can be used to good advantage with
any polyolefin sheet web for producing a wide variety of items.
Also, as will be explained, no pretreatment of the polyolefin
material to increase its surface energy is necessary to the
present invention, by virtue of the synergistic behavior of the
primer and adhesive layers.
The primer layer applied to the polyolefin substrate
comprises the dried residue of an initially liquid or flowable
coating composition which preferably includes a member selected
from the group consisting of the pressure sensitive adhesives,
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chlorinated polyolefins, copolymerized olefinic vinyl acetates,
and mixtures thereof. Mixtures of copolymerized olefinic vinyl
acetates and chlorinated polyolefins are especially advantageous,
and in the most preferred form the primer layer includes respec-
tive quantities of ethylene vinyl acetate and chlorinated poly-
olefin material. Preferably, the ratio of chlorinated polyolefin
to ethylene vinyl acetate is up to about 1:12, with the chlori-
nated polyolefin containing from about 15% to 46% by weight chlo-
rine and having a molecular weight of from about 3,000 to about
65,000. The ethylene vinyl acetate preferably has a vinyl ace-
tate content of from about 28% to 60% by weight and a melt index
(ASTM Method No. D1238) of from about 3 to 70. The most pre-
ferred primer coating composition comprises about a 25% solids by
weight dispersion in toluene, with the solids fraction comprising
about 3 parts ethylene vinyl acetate to about 1 part of chlori-
nated polyolefin material. This composition has been found to
provide an exceptionally strong bond between the substrate and
PVA remoistenable adhesive.
The outermost adhesive layer comprises the dried
residue of a water-based coating composition having a solids
fraction composed principally of polyvinyl alcohol dispersed in
water. Preferably, the adhesive composition solids fraction is
at least about 50% by weight partially hydrolyzed polyvinyl
alcohol. The overall coating composition is generally fairly
dilute, i.e., from about 75% to 96% by weight water. In the most
preferred form, the a &esive composition comprises about a 15%
solids by weight dispersion in water, with the solids fraction
comprising about 95% by weight partially hydrolyzed polyvinyl
alcohol (advantageously from about 70% to 90% hydrolyzed, most
preferably about 88% hydrolyzed) and about 5% by weight
polyvinyl pyrrolidone.
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In the production of a remoistenable ribbon, for
example, one or both of the opposed faces of the ribbon can be
coated with the primer and adhesive layers. This is generally
accomplished by sequentially applying and drying the primer and
adhesive compositions onto the web to effect bonding between ~he
substrate, primer layer and adhesive layer. In practice, each of
the layers can be applied by any conventional means, such as by
running the web through coating tanks and thereafter removing any
excess liquid material. The primer and adhesive coating compo-
sitions are generally applied hot, i.e., at a temperature of fromabout 120 F. to 230 F., and most advantageously from about
165 F. to 195 F. The web can then be squeegeed as it emerges
from the coating tanks in order to achieve a desirable thin layer
; of primer and adhesive composition. In this connection, a primer
-~ layer of from about 1/10 to 1 mil. in thickness is preferred,
with an adhesive layer of from about 1/4 to 1 mil. An adhesive
layer of below about 1/4 mil. can in some instances be excessive-
ly lubricious upon wetting and thus not suitable.
Drying of the initially liquid primer and adhesive
coating composition can be accomplished by any conventional
means, including drying in air at ambient temperatures. In the
preferred method, the primer composition is air-dried with hot
air at a temperature of up to about 300 F., while the adhesive
composition is similarly dried with air at a temperature from
about room temperature to about 250 F. It is to be understood,
however, that any conventional means known in the art of applying
coatings to web material could be used in applying the primer and
adhesive coatings.
The following example will illustrate the production of
remoistenable polyolefin ribbons in accordance with the inven-
tion, and also demonstrate the desirable remoistenable adhesive
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IN THE SPECIFICATION
properties thereof. The example is presented by way of
illustration only, and nothing therein should be taken as a
limitation upon the overall scope of the invention.
EXAMPLE
The following experiment was undertaken to demonstrate
the peel strengths of remoistenable adhesives in accordance with
the present invention, as compared with conventional systems.
Two separate tests were undertaken to measure com-
parative peel strengths. In each test 3/4-in.,wide chemically
foamed and monoaxially oriented polypropylene ribbons (0.005 in.
thick) were used as substrates. The ribbons were continuously
drawn through hot primer and adhesive coating baths with excess
solution being squeegeed off both sides of the ribbon as it
emerged from the coating baths. The ribbons were also hot-air
dried after both coating operations. The various coatings used
had compositions specified as follows:
Primer I: 25% solids solution of chlorinated polypro-
pylene in xylene (M.W.: 3,000-18% chlorine).
Primer II: 20% solids solution of chlorinated poly-
ethylene in toluene (M.W.: 50,000-46% chlorine).
Primer III: 25% solids solution of chlorinated polyethylene
in xylene (M.W.: 3,000-20% chlorine).
Primer IV: 25% solids solution of ethylene vinyl acetate,
- in toluene (42% vinyl acetate),
Primer V: 20% solids solution of ethylene vinyl acetate
in toluene (55% vinyl acetate?.
(Docket No. F-15617)
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Primer VI: 25% solution of general purpose, high tenacity
pressure sensitive silicone-based adhesive in
toluene.
Primer VII: 25% solids solution containing 1 part
chlorinated polypropylene in xylene (M.W.:
3,000-18% chlorine) and 3 parts ethylene vinyl
acetate in toluene (M.W.: 3,000-20% chlorine).
Primer VIII: 25% solids solution of chlorinated polypro-
pylene in xylene (M.W.: 3,000-18% chlorine).
20% solids solution of ethylene vinyl acetate
in toluene (55% vinyl acetate).
Primer IX: 20% solids solution of chlorinated poly-
ethylene in toluene (M.W.: 50,000-46% chlorine).
25% solids solution of ethylene vinyl acetate,
in toluene (42% vinyl acetate).
~dhesive I: 15% solution of 95 parts partially hydrolyzed
polyvinyl alcohol to 5 parts polyvinyl pyrrolidone.
Adhesive II: 25% solution of a conventional envelope adhesive
in water
Adhesive III: 50% solids solution of dextrin in water.
Standard: Pressure sensitive single surface adhesive
coated transparent tape. (All the tape was
manually applied over the primer layer.
` 40
The above primer and adhesive compositions were
applied in equal thicknesses and under identical conditions
during all tests, save for the adhesive standard which was simply
pressed onto the substrate in the normal manner~ Peel strengths
were measured by moistening a 3/4-in. length of the coated ribbon
sample and pressing the moistened section onto a similar un-
moistened length of the same sample, Five specimens each were
thus prepared and allowed to oven dry at 90 C~ for 60 minutes,
The non-adhered ends of each specimen were placed in clamps, one
retractable and one attached to a Hunter Model LKE.-05 force gauge ?
and pulled at a rate of 2 ft,tmin. The maximum force registered,
as the bond was peeled apart, was recorded for each sample and
the average computed. These results are shown in Table I
below:
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TABLE I
PEEL STRENGTHS
Test 1
Peel Strength
Primer Adhesive m/in. %l
None I 179 100
None Standard 399 223
I I 596 336
II I 396 222
III I 443 248
IV I 405 227
V I 377 211
VI I 495 277
VII I 505 283
VIII I 651 364
IX I 371 207
Test 2
Peel Strength
Primer Adhesive gm/in. - 701
VII I 339 244
VII II 108 78
VII III 127 91
None I 139 100
None II 0 0
None III 0 0
None Standard 314 227
Percentage peeI strength based upon no primer and adhesive
coat I as 100%.
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Test 1 illustrates that the best peel strengths were
obtained using primer VIII with a&esive coat I. However, all
other combinations are in the range of valuable and usable
strengths. Hence, it will be clear that essentially any primer
having the characteristics of bonding to both the substrate and
covering adhesive are usable in the present invention. Test 2
illustrates that the PVA adhesive coat has some peel strength
even on untreated polypFopylene substrate, whereas the other two
top coats do not. Further, use of one of the preferred primer
formulations increased the peel strength of the top coat, as with
Test 1. Therefore, it is clear that a type of synergism is
demonstrated through the use of primer and adhesive coats in
accordance with the invention, and particularly among the most
preferred chlorinated polyolefins, ethylene vinyl acetates and
polyvinyl alcohols employed in the respective layers.
Although not completely understood, it is hypothesized
that this synergism obtains in the preferred embodiment by
virtue of the chemicàl similarity of the polypropylene substrate
and chIorinated polyolefins in the primer coating that makes
possible a firm bond between the substrate and primer. On the
other hand, the chemical similarity between the copolymerized
olefinic vinyl acetate of the primer coating and the polyvinyl
alcohol of the remoistenable adhesive coating ensures that an
adequate bond is established between the primer and adhesive
layers.
It will also be seen that the peel strengths recorded
match or exceed those recorded using the standard tape. This
implies that the remoistenabIe adhesive applied is essentially
equal or better than the standard tape in terms of peel strength,
and thus the utility of the present invention s manifest.
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